Multi-feed detection apparatus, sheet conveyance apparatus, and sheet processing apparatus

ABSTRACT

A multi-feed detection apparatus may include an ultrasonic transmission unit, arranged on one side of a conveyance path configured to convey a sheet-like member, for transmitting an ultrasonic wave toward the conveyance path, an ultrasonic reception unit, arranged on the other side of the conveyance path, for receiving the ultrasonic wave from the ultrasonic transmission unit, and a multi-feed determination unit for determining, based on the reception result of the ultrasonic wave received by the ultrasonic reception unit, whether multi-feed of sheet-like members has occurred. The ultrasonic transmission surface of the ultrasonic transmission unit is inclined with respect to the conveyance path, and the ultrasonic reception surface of the ultrasonic reception unit is arranged to be almost parallel to the conveyance path.

This application is a continuation of International Patent ApplicationNo. PCT/JP2012/004050 filed on Jun. 22, 2012, and claims priority toJapanese Patent Application No. 2011-143761 filed on Jun. 29, 2011, theentire content of both of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multi-feed detection apparatus whichis mounted in an image processing apparatus such as a copying machine,scanner, facsimile machine, or printer, and detects whether multi-feedof a plurality of sheets has occurred, a sheet conveyance apparatusincluding the multi-feed detection apparatus, and a sheet processingapparatus such as an image reading apparatus or image forming apparatus.

2. Description of the Related Art

A scanner, printer, copying machine, printing machine, ATM (AutomatedTeller Machine), and the like have a mechanism of separating andconveying sheet-like members one by one. However, multi-feed may occur,in which when only one sheet-like member should be conveyed, two or moresheet-like members are conveyed while overlapping each other partiallyor entirely. To prevent this, an apparatus which conveys a sheet-likemember requires a function of detecting multi-feed of sheet-likemembers. As the mechanism of detecting multi-feed of sheet-like members,a multi-feed detection apparatus using an ultrasonic wave has prevailed.

In the multi-feed detection apparatus, it is known that when asheet-like member is irradiated with an ultrasonic wave, the ultrasonicwave is partially reflected by the sheet surface and the reflected waveis diffusely reflected between the sheet surface and an ultrasonictransmitter. An ultrasonic receiver sometimes receives the diffuselyreflected wave as a noise component, and the noise component generatedby diffuse reflection degrades the sensor performance. To solve this, anarrangement of emitting an ultrasonic wave obliquely to the sheetsurface is employed (see Japanese Patent Laid-Open No. 2007-276965).

SUMMARY OF THE INVENTION

To emit an ultrasonic wave obliquely to the sheet surface, as in theJapanese Patent Laid-Open No. 2007-276965, the ultrasonic transmitterand ultrasonic receiver need to be arranged obliquely. However, sincethe sheet conveyance apparatus and the like are becoming compact moreand more, it is becoming difficult to obliquely introduce the ultrasonictransmitter and ultrasonic receiver to face each other in the compactsheet member conveyance apparatus.

The present invention has been made in consideration of the abovesituation, and provides a multi-feed detection apparatus advantageousfor downsizing of the apparatus without degrading the multi-feeddetection performance, a sheet conveyance apparatus, and a sheetprocessing apparatus.

According to the present invention, a multi-feed detection apparatus iscomprising an ultrasonic transmission unit, arranged on one side of aconveyance path configured to convey a sheet-like member, fortransmitting an ultrasonic wave toward the conveyance path, anultrasonic reception unit, arranged on the other side of the conveyancepath, for receiving the ultrasonic wave from the ultrasonic transmissionunit, and a multi-feed determination unit for determining, based on areception result of the ultrasonic wave received by the ultrasonicreception unit, whether multi-feed of sheet-like members has occurred,wherein an ultrasonic transmission surface of the ultrasonictransmission unit is inclined with respect to the conveyance path, andan ultrasonic reception surface of the ultrasonic reception unit isarranged to be substantially parallel to the conveyance path.

According to the present invention, a multi-feed detection apparatus iscomprising an ultrasonic transmission unit, arranged on one side of aconveyance path configured to convey a sheet-like member, fortransmitting an ultrasonic wave toward the conveyance path, anultrasonic reception unit, arranged on the other side of the conveyancepath, for receiving the ultrasonic wave from the ultrasonic transmissionunit, and a multi-feed determination unit for determining, based on areception result of the ultrasonic wave received by the ultrasonicreception unit, whether multi-feed of sheet-like members has occurred,wherein the ultrasonic transmission unit and the ultrasonic receptionunit have different inclination angles with respect to the conveyancepath.

Further, the present invention may be applied to a sheet conveyanceapparatus in which the above-described multi-feed detection apparatus isarranged as a multi-feed detection unit in a conveyance apparatus mainbody configured to convey a sheet-like member along a conveyance path.Also, the present invention may be applied to a sheet processingapparatus such as an image reading apparatus including the sheetconveyance apparatus and an image reading unit for reading an image of asheet-like member conveyed by the sheet conveyance apparatus, or animage forming apparatus including the sheet conveyance apparatus and animage forming unit for forming an image on a sheet-like member conveyedby the sheet conveyance apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a view showing the schematic structure of a multi-feeddetection apparatus when viewed from the side;

FIG. 2 is a schematic view showing the arrangement of the main part ofthe multi-feed detection apparatus;

FIG. 3 is a block diagram showing the arrangement of signal processingin the multi-feed detection apparatus;

FIG. 4 is a schematic view showing the arrangement of the main part ofthe multi-feed detection apparatus;

FIG. 5 is a view showing the schematic structure of a multi-feeddetection apparatus when viewed from the side;

FIG. 6 is a block diagram showing the arrangement of signal processingin the multi-feed detection apparatus;

FIG. 7 is a view showing the schematic structure of the multi-feeddetection apparatus according to when viewed from the top;

FIG. 8 is a view showing the schematic arrangement of a multi-feeddetection apparatus when viewed from the side;

FIG. 9 is a view exemplifying the schematic arrangement of a sheetprocessing apparatus; and

FIG. 10 is a view exemplifying the schematic arrangement of the sheetprocessing apparatus.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be describedbelow in detail with reference to the drawings. It should be noted thatthe dimensions, materials, shapes, relative arrangement, and the like ofcomponents set forth in these embodiments do not limit the scope of thepresent invention unless it is specifically stated otherwise.

FIG. 1 is a view showing the schematic structure of a multi-feeddetection apparatus according to the first embodiment of the presentinvention when viewed from the side. FIG. 2 is a schematic view showingthe arrangement of the main part of the multi-feed detection apparatusaccording to the first embodiment of the present invention.

As shown in FIGS. 1 and 2, a multi-feed detection apparatus 10 accordingto the embodiment is an apparatus which is arranged on a conveyance pathconfigured to convey a sheet-like member (to be simply referred to as asheet member hereinafter) and detects, by an ultrasonic method,multi-feed in which a plurality of sheet members are conveyed whileoverlapping each other.

More specifically, as shown in FIG. 1, a conveyance path 11 forconveying a sheet member P while keeping it flat in the horizontaldirection is inserted in the sheet conveyance path. The conveyance path11 is covered with two conveyance guide plates 12 and 13, that is, theupper conveyance guide plate (conveyance path forming member) 12 on theupper surface side and the lower conveyance guide plate (conveyance pathforming member) 13 on the lower surface side which face each other via aflat conveyance space 11 a. In the multi-feed detection apparatus 10having this arrangement, an ultrasonic transmitter 20 is disposed as anultrasonic transmission (origination) unit above the conveyance path 11,and an ultrasonic receiver 30 is disposed as an ultrasonic receptionunit below it so that they face each other via the conveyance path 11.

When detecting multi-feed of sheet members by using an ultrasonic sensormade up of the transmitter 20 and receiver 30, the following detectionperformance unique to the ultrasonic wave is obtained:

(1) This arrangement detects multi-feed in a non-contact state withoutcontacting a sheet member, and does not hinder conveyance of a sheetmember.

(2) This arrangement can detect multi-feed regardless of the thicknessof a sheet member, and can detect even multi-feed in which sheet membersof different thicknesses coexist.

(3) This arrangement can detect multi-feed without the influence of thecolor of a sheet member, and does not require adjustment even if thecolor of a sheet member changes.

By using the ultrasonic sensor, multi-feed of sheet members can bedetected at high sensitivity. However, in some cases, when a sheetmember is irradiated with an ultrasonic wave, the ultrasonic wave ispartially reflected by the sheet surface and the reflected wave isdiffusely reflected between the sheet surface and the transmitter.Depending on the arrangement of the ultrasonic transmitter and receiver,the receiver sometimes receives the diffusely reflected wave as a noisecomponent, and the noise component generated by diffuse reflectiondegrades the sensor performance. To solve this, it is necessary toincline (give an angle) the ultrasonic wave traveling direction withrespect to the sheet member (conveyance path) so that the reflected waveis reflected in a direction different from the direction toward thetransmitter. In a high-directivity ultrasonic sensor, the transmissionsurface of the transmitter and the reception surface of the receiverneed to be arranged parallel to face straight each other. Under thecircumstances, it is very difficult to downsize the apparatus. To solvethis, the multi-feed detection apparatus 10 according to the embodimentdevises the arrangement and configuration of the ultrasonic receiver 30with respect to the conveyance path 11, and the like, details of whichwill be described later.

More specifically, the ultrasonic transmitter 20 is attached to asubstrate 21 having a fixing member to a main body apparatus (notshown), and a circuit board including a driving circuit and the like.The receiver 30 is also attached to a substrate 31 having a fixingmember to the main body apparatus (not shown), and a circuit boardincluding an amplifier circuit and the like.

An entrance port (through hole) 12 a is formed at the crossing positionof the upper conveyance guide plate 12 where the upper conveyance guideplate 12 crosses the ultrasonic transmission direction of thetransmitter 20. An ultrasonic transmission surface 20 a of thetransmitter 20 emits an ultrasonic wave U in an obliquely downwardtransmission direction. The emitted ultrasonic wave U enters theconveyance space 11 a in the conveyance path 11 via the entrance port 12a formed in the upper conveyance guide plate 12, and irradiates thesheet member P passing through the conveyance space 11 a.

The transmitter 20 takes an arrangement form in which the transmissiondirection is suited to transmit the ultrasonic wave U, as represented byan incline θu with respect to the sheet member P. By setting thetransmission direction of the transmitter 20 obliquely to the sheetmember P, the ultrasonic wave U transmitted by the transmitter 20 isreflected by the surface of the sheet member P, and a reflected wave Rtravels in a direction different from the direction toward thetransmitter 20 and does not return to the transmitter 20. Accordingly,generation of a noise component such as an interference acoustic wave orreverberant acoustic wave can be reduced between, for example, thetransmitter 20 and the sheet member P.

An exit port 13 a is formed at the crossing position of the lowerconveyance guide plate 13 where the lower conveyance guide plate 13crosses the ultrasonic reception direction of the receiver 30. Note thatthe area of the exit port 13 a formed at the crossing position of thelower conveyance guide plate 13 is suitably set to be almost equal to orsmaller than the area of an ultrasonic reception surface 30 a of thereceiver 30 and be larger than half the area of the reception surface 30a in order to prevent entrance of dust and the like, as long as thereception performance can be maintained. Hence, mixing of paper dust andthe like from the exit port 13 a can be suppressed to reduce theinfluence on reception of an ultrasonic wave.

The receiver 30 is arranged to be almost parallel (including parallel)to the conveyance path 11 (sheet member P). In the embodiment, an angleθu′ is set to be θu′≈90°. This is because the sound pressure of anultrasonic wave U′ having passed through the sheet member P becomessufficiently low and a large interference hardly occurs between thereceiver 30 and the sheet member P. The arrangement in which thereceiver 30 is arranged to be almost parallel to the conveyance path 11includes, for example, a state in which the reception surface 30 abecomes a surface parallel to or slightly inclined with respect to theconveyance path 11 while facing the conveyance path 11. This arrangementalso includes a state in which the reception surface 30 a of thereceiver 30 substantially faces the transmission surface 20 a of thetransmitter 20 when viewed from the transmission surface 20 a of thetransmitter 20. The directivity of the ultrasonic wave U′ slightlydecreases when the ultrasonic wave U′ passes through the sheet member P.Considering this, the angle of the receiver 30 may be changed to bealmost parallel to the sheet member P. That is, the transmitter 20 andreceiver 30 are arranged to satisfy a relation of θu<θu′≈90°. Inaddition, the receiver 30 is preferably a MEMS (Micro Electro MechanicalSystem) ultra-compact ultrasonic receiver with low directivity. Evenwhen such an ultra-compact ultrasonic receiver is used and combined witha high-directivity ultrasonic transmitter, the receiver 30 (receptionsurface 30 a) can reliably receive an ultrasonic wave from thetransmitter 20 even if the receiver 30 is downsized, because thetransmission surface 20 a of the transmitter 20 substantially faces thereception surface 30 a of the receiver 30.

The MEMS element structure is not particularly limited, but preferablyincludes a MEMS element which includes an ultrasonic receiver of a plateshape or the like with an ultrasonic reception surface and a holdingportion for holding the ultrasonic receiver, and is formed on asubstrate such as a silicon substrate. By using a microfabricationtechnique for a substrate of a silicon material or the like, a desiredstructure can be relatively easily fabricated, implementing anultra-compact receiver.

If such a MEMS sensor chip is applied to the receiver 30, the receptionsurface and mounting substrate can be substantially downsized, comparedto a conventional ultrasonic receiver. For this reason, the amount ofultrasonic wave reflected by the ultrasonic reception surface andmounting substrate surface becomes smaller than that in the conventionalultrasonic receiver. Since a reflected wave generated between the sheetmember P and the receiver 30 is reduced, preferable detectionperformance can be obtained even if the sheet member P and receptionsurface 30 a are arranged to be almost parallel. Note that the MEMSreceiver preferably has a smooth frequency characteristic and asensitivity in a wide frequency range. Therefore, it is preferable touse the MEMS sensor for the receiver because a change of the ultrasonicfrequency to be received can be satisfactorily coped with by changing afiltering circuit & amplifier circuit and determination circuit at asubsequent stage.

As described above, the receiver 30 is arranged on the substrate 31having a fixing member to the main body apparatus (not shown), and acircuit board including an amplifier circuit and the like. Since thereceiver 30 can be arranged to be almost parallel to the conveyance path11, various merits are obtained: the receiver 30 need not be arranged onthe substrate 31 with a large inclination, the receiver 30 can be easilymounted on the substrate 31, and the mounting space can be reduced.

In the multi-feed detection apparatus 10 according to the embodiment,the inclination angles of the transmitter 20 and receiver 30 withrespect to the conveyance path 11 are different. More specifically, theultrasonic transmission surface 20 a of the transmitter 20 is arrangedto be inclined with respect to the conveyance path 11. The ultrasonicreception surface 30 a of the receiver 30 is arranged to be almostparallel to the conveyance path 11. Thus, the multi-feed detectionperformance does not degrade, and the apparatus can be greatly downsizedthanks to reduction of the installation space of the receiver 30. Whenexamining a structure in which the receiver 30 is mounted in theapparatus main body, the degree of freedom of the design can beincreased, and the product or manufacturing cost can be greatly reduced.

In the above-described embodiment, the outer shape of the receiver 30serving as an ultrasonic reception unit is preferably set to be smallerthan that of the transmitter 20 serving as an ultrasonic transmissionunit. For example, the ultrasonic reception surface 30 a (area of thereception region) of the receiver 30 is desirably set to be smaller thanthe ultrasonic transmission surface 20 a (area of the transmissionregion) of the transmitter 20. The use of the MEMS microelement as thereceiver 30 is not only advantageous for downsizing of the apparatus,but also widens the directivity on the receiving side (increases theultrasonic reception sensitivity). By combining the MEMS microelementwith the high-directivity transmitter 20, desired multi-feed detectionperformance can be ensured. In this arrangement, the ultrasonicreception surface 30 a of the receiver 30 is positioned in a regionwhere it faces the ultrasonic transmission surface 20 a of thetransmitter 20. The implementation of this positional relationship isadvantageous for downsizing of the apparatus, and facilitatespositioning (attachment) of the receiver 30 with respect to thetransmitter 20. This can increase the degree of freedom of the design,improve the assembly accuracy, and reduce the manufacturing cost.

Further, in the present invention, the opening area of the entrance portof the upper conveyance guide plate is preferably set to be smaller thanthe ultrasonic transmission surface of the transmitter. That is, acondition that the size (opening area) of the entrance port throughwhich an ultrasonic wave enters the conveyance path from the ultrasonictransmission surface is smaller than the area of the ultrasonictransmission surface (for example, a condition to satisfy a relation of[size of the ultrasonic transmission surface]>[size of theoriginating-side conveyance path hole (opening)]≧[size of thereceiving-side conveyance path hole (opening)]≧[size of the ultrasonicreception surface]) is preferably set. This can effectively preventdegradation of the multi-feed detection performance by the reflectedwave of an ultrasonic wave in the conveyance path.

The control arrangement of the above-described multi-feed detectionapparatus 10 will be explained in detail with reference to FIG. 3. FIG.3 is a block diagram showing a control circuit assembled in themulti-feed detection apparatus. The multi-feed detection apparatus 10according to the embodiment includes, on the ultrasonic transmittingside, an oscillation circuit 22 serving as a signal generation unit forgenerating a signal of a predetermined frequency (for example, 300 kHz),and an amplifier circuit 23 serving as a signal amplification unit foramplifying a signal from the oscillation circuit 22. The multi-feeddetection apparatus 10 includes, on the ultrasonic receiving side, afilter & amplifier circuit 32 which removes noise and amplifies areceived signal, and a determination circuit 33 serving as a multi-feeddetermination unit for comparing a received signal with a referencevalue to make a determination.

An electrical signal of the predetermined frequency output from theoscillation circuit 22 is amplified by the amplifier circuit 23 to havea predetermined value, then is input to the transmitter 20, andconverted into an ultrasonic wave U by an ultrasonic generation elementin the transmitter 20. The converted ultrasonic wave U is radiatedtoward the receiver 30 via the sheet member P conveyed through theconveyance path 11.

The ultrasonic wave U emitted by the transmitter 20 impinges on thesheet member P conveyed in the conveyance path 11, and is partiallyradiated outside as the reflected wave R. The ultrasonic wave U′ havingpassed through the sheet member P is received by the receiver 30, andconverted into an electrical signal by the piezoelectric element or MEMSelement of the receiver 30. The signal converted into the electricalsignal is processed by the filter circuit & amplifier circuit 32 havingthe filter function of removing noise and the amplification function. Bycomparison with a threshold, the determination circuit 33 determineswhether one sheet member P has been conveyed or a plurality of sheetmembers P have been conveyed. Based on the result, the determinationcircuit 33 detects the presence/absence of multi-feed of the sheetmembers P. Note that this determination signal is sent to a sheet memberconveyance control system (for example, a control unit such as a CPU)(not shown).

As described above, in the multi-feed detection apparatus 10 accordingto the embodiment, the ultrasonic receiver 30 is arranged to be almostparallel to the conveyance path 11 through which the sheet member P isconveyed. Compared to a conventional arrangement, the size in thedirection of height can be reduced, greatly downsizing the apparatus.Especially when the structure of the ultrasonic receiver is downsized bythe MEMS technique, as shown in FIG. 4, a MEMS receiver 30′ andsubstrate 31′ can be arranged without taking up space in the verticaldirection in FIG. 4 by bringing them close to the conveyance path 11 tobe almost parallel. This is further effective in downsizing of theapparatus. FIG. 4 exemplifies a structure in which the outer shape ofthe receiver 30′ serving as an ultrasonic reception unit is set to besmaller than that of the transmitter 20′ serving as an ultrasonictransmission unit. In the structure of FIG. 4, the outer shape of thereceiver 30′ is set to be small, so the opening area of the exit port 13a can be decreased. Mixing of paper dust and the like can be effectivelysuppressed, and the influence on ultrasonic detection can be effectivelyreduced.

In a piezoelectric vibration ultrasonic sensor, the ultrasonic resonancefrequency in the element is fixed, and it is difficult to generate anultrasonic wave of another frequency. Under the physical condition, theultrasonic frequency usable in a pair of ultrasonic sensors is one type.In the ultrasonic multi-feed detection method, an ultrasonic wave isapplied to a sheet member, and multi-feed is determined from theintensity of the ultrasonic wave having passed through the sheet member.In an ultrasonic multi-feed detection unit having a high oscillationfrequency around 300 kHz, when multi-feed of very thin sheet membersoccurs, the signal appropriately attenuates, and the multi-feed can benormally detected. However, for very thick sheet members, attenuation bythe sheet members becomes large, and multi-feed may be erroneouslydetected. To the contrary, in an ultrasonic multi-feed detection unithaving a low oscillation frequency around 200 kHz, attenuation by sheetmembers becomes small, and multi-feed may be erroneously detected forthin sheet members. If piezoelectric ceramic is used in the ultrasonicoscillation unit and reception unit, the resonance frequency of theultrasonic oscillator and ultrasonic receiver is fixed to the resonancefrequency of the piezoelectric ceramic used and the acoustic matchinglayer, and cannot be changed. Even if a driving voltage of a frequencydeviating from this resonance frequency is applied, no satisfactoryoscillation amplitude can be obtained, and separate ultrasonicoscillators having adjusted resonance frequencies need to be prepared inaccordance with necessary ultrasonic frequencies.

To avoid this, the present invention implements an arrangement in whicha plurality of ultrasonic frequencies are used in accordance with thematerials of sheet members. An arrangement in which a plurality ofultrasonic frequencies are used in addition to the arrangement of thefirst embodiment will be explained in detail by citing an embodiment.

FIG. 5 is a schematic view showing an arrangement near a sheet membermulti-feed detection apparatus incorporated in an image readingapparatus or the like. In FIG. 5, the same reference numerals as thosein FIG. 1 denote the same parts, and a repetitive description thereofwill be omitted.

As shown in FIG. 5, a multi-feed detection apparatus 10A includes aconveyance path 11 for conveying a sheet member P while keeping it flatin the horizontal direction in FIG. 5. The conveyance path 11 is coveredwith two conveyance guide plates 12 and 13, that is, the upperconveyance guide plate 12 on the upper surface side and the lowerconveyance guide plate 13 on the lower surface side which face eachother via a flat conveyance space 11 a.

In the multi-feed detection apparatus 10A, a plurality of transmitters20A and 20B are disposed above the conveyance path 11, and a receiver30A is disposed below it so that they face each other via the conveyancepath 11. The transmitter 20A emits an ultrasonic wave U1 to a sheetmember, and the transmitter 20B emits an ultrasonic wave U2 to the sheetmember P. The transmitters 20A and 20B are configured to transmitultrasonic waves of different frequencies.

An entrance port 12 a is formed at the crossing position of the upperconveyance guide plate 12 where the upper conveyance guide plate 12crosses the ultrasonic wave U1 from the transmitter 20A and theultrasonic wave U2 from the transmitter 20B. The transmitters 20A and20B forming an ultrasonic sensor take an arrangement form in which theultrasonic transmission directions are set obliquely to the sheet memberP and suited to transmission of the ultrasonic waves U1 and U2. Inparticular, f1 is the frequency of the ultrasonic wave U1 of thetransmitter 20A, f2 is the frequency of the ultrasonic wave U2 of thetransmitter 20B, θ1 is an internal angle formed by the ultrasonic waveU1 and sheet member P, and θ2 is an internal angle formed by theultrasonic wave U2 and sheet member P. Similar to the first embodiment,the ultrasonic transmission directions of the transmitters 20A and 20Bare set obliquely to the sheet member P to reduce reflection and theinfluence on reverberant noise. The ultrasonic waves U1 and U2 emittedby the transmitters 20A and 20B impinge on the sheet member P conveyedin the lower conveyance guide plate 13, and are partially reflected.

Here, θ1<θ2, and θ1≠θ2. Thus, an ultrasonic wave reflected by the sheetmember P has an angle deviated from the perpendicular of thetransmission surface of the facing other transmitter. The ultrasonicwave reflected again by the transmission surface of the othertransmitter mentioned above is reflected in a direction different fromthe direction toward the entrance port 12 a serving as an opening. Theultrasonic wave U1 or U2 is not multiple-reflected and does not serve asa noise factor.

In this manner, according to the embodiment, as for the two transmitters20A and 20B, the inclination angle of the ultrasonic transmissionsurface of one transmitter 20A with respect to the conveyance path 11 isset to be larger than that of the ultrasonic transmission surface of theother transmitter 20B. This can effectively prevent multiple reflectionof ultrasonic waves transmitted (originated) by the transmitters 20A and20B, and can prevent generation of noise.

In the embodiment, if f1<f2, a relation of θ1<θ2 desirably holds. Thisis because, as the frequency of an ultrasonic wave increases, theattenuation amount upon passing through a sheet member increases, and atthe same time the directivity is enhanced. Therefore, the transmittersare arranged so that the receiver 30A can easily receive an ultrasonicsignal of a high frequency which readily attenuates.

More specifically, in the embodiment, the ultrasonic transmission unitincludes a plurality of ultrasonic transmission unit (transmitters 20Aand 20B) having different ultrasonic transmission frequencies. Theultrasonic transmission surface of the transmitter 20B having a highultrasonic transmission frequency is arranged at a larger inclinationangle (relation of θ1<θ2) with respect to the conveyance path 11 thanthe ultrasonic transmission surface of the transmitter 20A having a lowultrasonic transmission frequency. Hence, the receiver 30A can easilyreceive an ultrasonic signal of a high frequency which readilyattenuates. This can improve the multi-feed detection performance.

As described above, according to the embodiment, downsizing is achievedby arranging the ultrasonic reception surface of the receiver 30Aserving as an ultrasonic reception unit to be almost parallel to theconveyance path 11. A plurality of transmitters 20A and 20B are arrangedfor one receiver 30A. The inclination angle of the ultrasonictransmission surface of one transmitter 20B with respect to theconveyance path 11 is set to be larger than that of the ultrasonictransmission surface of the other transmitter 20A. The multi-feeddetection performance can be improved while achieving downsizing.

FIG. 6 is a block diagram showing the control circuit of the ultrasonicsensor assembled in the multi-feed detection apparatus 10A. In thisarrangement, the transmitting side includes oscillation circuits 22A and22B which generate a signal of a predetermined frequency f1 (forexample, 200 kHz) and a signal of a predetermined frequency f2 (forexample, 300 kHz), and amplifier circuits 23A and 23B which amplify thesignals of the predetermined frequencies. The oscillation circuits 22Aand 22B and the amplifier circuits 23A and 23B are connected incorrespondence with the transmitters 20A and 20B, respectively. Theoscillation circuits 22A and 22B may be configured to use variableorigination circuits capable of changing the frequency in accordancewith an external signal, amplify the variable oscillation signals, andfinally select either the transmitter 20A or 20B. This circuitconfiguration includes a transmitter selection unit.

The receiver 30A converts an ultrasonic wave having passed through thesheet member P into an electrical signal. Filter circuits & amplifiercircuits 32 a and 32 b having the filter function of removing noise andthe amplification function process the signal converted into theelectrical signal. The filter circuits & amplifier circuits 32 a and 32b have different frequency filters and different amplification factors.For example, the filter circuit & amplifier circuit 32 a gives optimaladjustment to the ultrasonic wave U1 transmitted from the transmitter20A, and the filter circuit & amplifier circuit 32 b gives optimaladjustment to the ultrasonic wave U2 transmitted from the transmitter20B. This can be implemented by changing the reception signalamplification condition based on the frequency of an ultrasonic wavetransmitted from at least one of the transmitters 20A and 20B serving asa plurality of ultrasonic wave transmission unit.

In addition, the above-described control block arrangement includesdetermination circuits 33 a and 33 b which receive electrical signalsfrom the filter circuits & amplifier circuits 32 a and 32 b, comparethem with reference values, and make determinations. Also in thedetermination circuits 33 a and 33 b, different determination methodsand references are desirably set in accordance with the frequencies ofultrasonic waves. For example, the determination circuit for thehigh-frequency ultrasonic wave U1 performs voltage comparison with apredetermined threshold. The determination circuit for the low-frequencyultrasonic wave U2 performs phase comparison with a predetermined phase,in addition to voltage comparison with a predetermined threshold. Theresults of these determinations are integrated and sent to a sheetmember conveyance control system (not shown). Note that a filter circuit& amplifier circuit and determination circuit to be used among those ofa plurality of systems may be changed in accordance with a transmitterto be used among a plurality of transmitters.

As another example, the filter circuit & amplifier circuit may be formedfrom one circuit by using a circuit capable of changing the filteringfrequency and amplification factor. Further, the determination circuitmay be configured digitally or a program on the CPU, and thedetermination method and determination level may be changed, as needed.As shown in FIG. 6, the plurality of transmitters (oscillators) 20A and20B may be set on a plane parallel to the sheet member conveyance plane,and the receiver may be arranged at an angle in the ultrasonicorigination direction about the axis.

FIG. 7 is a view showing another multi-feed detection apparatus whenviewed from a direction perpendicular to the sheet member conveyanceplane. The transmitters 20A and 20B are arranged at an inner angle αwith respect to the entrance port 12 a when viewed from above the upperconveyance guide plate 12. When α≠180°, even if θ1 and θ2 mentionedabove satisfy θ1=θ2, no multiple reflection occurs. As for the number oftransmitters, two or more transmitters may be arranged as long as theyare arranged to prevent multiple reflection. In this manner, a pluralityof ultrasonic transmitters having different frequencies are used, andthe ultrasonic frequency is changed in accordance with a sheet member tobe conveyed, thereby executing more appropriate sheet member multi-feeddetermination. If the transmitters 20A and 20B serving as ultrasonictransmission unit are arranged at different ultrasonic transmissionangles with respect to the receiver 30A when viewed from a directionperpendicular to the ultrasonic reception surface of the receiver 30Aserving as one ultrasonic reception unit, more appropriate sheet membermulti-feed determination can be implemented. In particular, thetransmitters 20A and 20B may be arranged with a positional relationshipin which the respective ultrasonic transmission directions to onereceiver 30A become perpendicular to each other.

As described above, in the multi-feed detection apparatus 10A accordingto the embodiment, the directivity of an ultrasonic wave slightlydecreases after the ultrasonic wave passes through a sheet-like member,and the directivity is improved by downsizing the receiver(receiving-side element structure) 30A. In consideration of them, theangle of the receiver with respect to the conveyance path 11 isappropriately changed (more specifically, the receiver is arranged to bealmost parallel), and the installation size of the multi-feed detectionsensor can be reduced. By appropriately changing the angle on the sideof the receiver 30A, a plurality of elements can be arranged on the sideof the transmitters 20A and 20B, multi-feed detection can be executed ata plurality of ultrasonic frequencies, and multi-feed detection becomespossible for various types of sheet members. More specifically, byexecuting multi-feed detection at a plurality of ultrasonic frequencies,accurate multi-feed detection can be performed without a malfunctionregardless of a change of the thickness of the sheet member, the coatingstate of the sheet member surface, and a change of the material of thesheet member.

In the multi-feed detection apparatuses according to the first andsecond embodiments described above, the multi-feed detectionconfiguration is constructed by arranging the transmitter above theconveyance path and arranging the receiver below the conveyance path.However the present invention is not limited to this, as a matter ofcourse. For example, the arrangement of the ultrasonic transmitter andreceiver may be reversed. That is, as shown in FIG. 8, the ultrasonictransmitter 20 may be arranged below the conveyance path 11 to originatean ultrasonic wave upward, and the facing receiver 30 may be arrangedabove the conveyance path 11. At this time, similar to the first andsecond embodiments described above, the ultrasonic reception surface ofthe receiver 30 is set to be almost parallel to the conveyance path 11.This can effectively avoid a situation in which multi-feed detection ishindered by a foreign substance such as paper dust generated byconveyance of a sheet member along the conveyance path 11. Especiallywhen a MEMS element is used as the receiver 30, the receiver 30 (and thethrough hole in the conveyance path forming plate on the receiving side)can be relatively downsized, compared to the transmitter 20 (and thethrough hole in the conveyance path forming plate on the transmittingside). Considering the influence of attachment of a foreign substancesuch as paper dust to the ultrasonic reception surface, the receiver 30is desirably arranged above the conveyance path 11 (for example, theupper side in the direction of gravity (upper side in the verticaldirection in FIG. 8) with respect to the conveyance path 11), as shownin FIG. 8. This can contribute to downsizing of the multi-feed detectionapparatus, and the multi-feed detection performance can be maintainedmore stably.

FIG. 9 is a view exemplifying another arrangement of a sheet-like memberconveyance apparatus including the multi-feed detection apparatusaccording to the present invention.

In FIG. 9, reference numeral 801 denotes an image reading apparatus mainbody (to be referred to as a sheet-like member conveyance apparatus mainbody hereinafter) serving as a sheet-like member conveyance apparatusincluding the multi-feed detection apparatus 10 described in the firstor second embodiment. Reference numeral 802 denotes a sheet feed port;803, a sheet feed tray; 804, an operation unit; 805, a discharge port;and 806, a discharge tray.

When scan instruction information is input from the operation unit 804,sheet-like members (not shown) serving as objects stacked on the sheetfeed tray 803 are conveyed one by one into the sheet-like memberconveyance apparatus main body 801 via the sheet feed port 802. Imageinformation of the sheet-like member conveyed inside the sheet-likemember conveyance apparatus main body 801 is read by an image readingsensor (not shown). After that, the sheet-like member is conveyed in thedischarge direction, and discharged from the sheet-like memberconveyance apparatus main body 801 via the discharge port 805.Sheet-like members discharged from the sheet-like member conveyanceapparatus main body 801 are sequentially stacked on the discharge tray806.

FIG. 10 is a sectional view showing the internal structure of thesheet-like member conveyance apparatus main body 801 shown in FIG. 9. InFIG. 10, the same reference numerals as those in FIG. 9 denote the sameparts.

In FIG. 10, reference numeral 901 denotes a feed roller; and 902, aretard roller including a torque limiter 903 between the retard roller902 and a rotating shaft. By the action of the feed roller 901 andretard roller 902, sheet-like members 201 stacked on the sheet feed tray803 are separated one by one, and conveyed into the sheet-like memberconveyance apparatus main body 801 via the sheet feed port 802 in adirection indicated by the arrow B in FIG. 10. Reference numerals 904denote conveyance rollers which further convey, toward the dischargeport 805, sheet-like members conveyed one by one by the action of thefeed roller 901 and retard roller 902.

Reference numeral 905 denotes an image reading unit (reverse surfaceimage reading unit) which reads the reverse surface of a sheet-likemember. Reference numeral 906 denotes an image reading unit (obversesurface image reading unit) which reads the obverse surface of asheet-like member. The image reading units 905 and 906 configure adouble-sided image reading unit. Each of the reverse surface imagereading unit 905 and obverse surface image reading unit 906 incorporatesa light source (not shown) for irradiating a sheet-like member, and animage reading sensor (not shown) for reading image information of asheet-like member. The double-sided image reading unit reads the imageof a sheet-like member at a reading position A in FIG. 11. Referencenumeral 907 denotes a first platen roller which presses a conveyedsheet-like member to bring it into tight contact with the reversesurface image reading unit 905 at the reading position A. Referencenumeral 908 denotes a second platen roller which presses a conveyedsheet-like member to bring it into tight contact with the obversesurface image reading unit 906 at the reading position A.

Reference numerals 909 denote discharge rollers which discharge aconveyed sheet-like member from the sheet-like member conveyanceapparatus main body 801 via the discharge port 805. Reference numeral910 denotes a conveyance driving source which is a conveyance motor ingeneral. The conveyance driving source 910 is connected to the rotatingshaft of each roller described above by a gear mechanism or beltmechanism (neither is shown). When the conveyance driving source 910rotates, each roller described above rotates to convey a sheet-likemember in a predetermined direction at a predetermined speed. When theconveyance driving source 910 rotates clockwise in FIG. 11, thesheet-like member is conveyed from the sheet feed port 802 to thedischarge port 805. Reference numeral 911 denotes an original detectionsensor which detects whether there is a sheet-like member in the sheetfeed port 802. Reference numeral 912 denotes a pre-feed detection sensorwhich detects the end of a conveyed sheet-like member.

An ultrasonic originating unit 103 and ultrasonic receiving unit 104 arearranged upstream side of the conveyance rollers 904 to detect themulti-feed state of fed sheet-like members. The ultrasonic originatingunit 103 and ultrasonic receiving unit 104 are arranged to face eachother via a sheet-like member conveyance path so that an ultrasonic waveoriginated by the ultrasonic originating unit 103 can pass through asheet-like member serving as a multi-feed detection target and bereceived by the ultrasonic receiving unit 104. A multi-feed detectionunit including the ultrasonic originating unit 103 and ultrasonicreceiving unit 104 is applicable to the multi-feed detection apparatusaccording to the first or second embodiment described above.

Note that the ultrasonic originating unit 103 and ultrasonic receivingunit 104 may be arranged downstream of the conveyance rollers 904.

In addition to the above-described embodiments, the present invention iswidely applied to an arrangement including at least one of the followingarrangements in a multi-feed detection apparatus including an ultrasonictransmission unit, arranged on one side of a conveyance path configuredto convey a sheet-like member, for transmitting an ultrasonic wavetoward the conveyance path, an ultrasonic reception unit, arranged onthe other side of the conveyance path, for receiving the ultrasonic wavefrom the ultrasonic transmission unit, and a multi-feed determinationunit for determining, based on the reception result of the ultrasonicwave received by the ultrasonic reception unit, whether multi-feed ofsheet-like members has occurred:

(1) a structure in which the ultrasonic reception unit is arranged tohave an outer shape smaller than that of the ultrasonic transmissionunit.

(2) a structure in which the ultrasonic reception surface of theultrasonic reception unit is smaller than the ultrasonic transmissionsurface of the ultrasonic transmission unit.

(3) a structure in which the ultrasonic reception surface of theultrasonic reception unit is smaller than the ultrasonic transmissionsurface of the ultrasonic transmission unit and is positioned in aregion where the ultrasonic reception surface faces the ultrasonictransmission surface.

(4) a structure in which the multi-feed detection apparatus includes aconveyance path forming plate configured to separate the ultrasonictransmission unit from the conveyance path and form at least part of theconveyance path, a through hole is formed at a portion of the conveyancepath forming plate that faces the ultrasonic transmission unit, and theopening of the through hole is smaller than the ultrasonic transmissionsurface of the ultrasonic transmission unit.

In the multi-feed detection apparatus having at least one of structures(1) to (4), the ultrasonic reception unit becomes relatively smallerthan the ultrasonic transmission unit. The apparatus can be downsized,the degree of freedom of the design can be increased, and the cost ofthe apparatus can be reduced.

Although the structure of the sheet-like member conveyance apparatusincluding the multi-feed detection apparatus according to the presentinvention has been exemplified, the multi-feed detection apparatusaccording to the present invention is applicable to another form as longas the apparatus conveys a sheet-like member. For example, themulti-feed detection apparatus according to the present invention can besimilarly arranged in a scanner, printer, copying machine, facsimilemachine, printing machine, ATM (Automated Teller Machine), and the like.

The present invention is not limited to the above-described embodiments,and various modifications (including organic combinations of theembodiments) can be made based on the gist of the present invention andare not excluded from the scope of the present invention. Note that thepresent invention includes all arrangements as combinations of theabove-describe embodiments and their modifications.

What is claimed is:
 1. A multi-feed detection apparatus comprising: anultrasonic transmission unit, arranged on one side of a conveyance pathconfigured to convey a sheet-like member, for transmitting an ultrasonicwave toward the conveyance path; an ultrasonic reception unit, arrangedon the other side of the conveyance path, for receiving the ultrasonicwave from said ultrasonic transmission unit; and a multi-feeddetermination unit for determining, based on a reception result of theultrasonic wave received by said ultrasonic reception unit, whethermulti-feed of sheet-like members has occurred, wherein an ultrasonictransmission surface of said ultrasonic transmission unit is inclinedwith respect to the conveyance path, and an ultrasonic reception surfaceof said ultrasonic reception unit is arranged to be substantiallyparallel to the conveyance path.
 2. The multi-feed detection apparatusaccording to claim 1, wherein said ultrasonic transmission unit includesa plurality of ultrasonic transmission unit arranged for said oneultrasonic reception unit.
 3. The multi-feed detection apparatusaccording to claim 2, wherein the ultrasonic transmission surface ofsaid one ultrasonic transmission unit has a larger inclination anglewith respect to the conveyance path, compared to the ultrasonictransmission surfaces of said remaining ultrasonic transmission unit. 4.The multi-feed detection apparatus according to claim 2, wherein saidultrasonic transmission unit includes a plurality of ultrasonictransmission unit having different ultrasonic transmission frequencies,and the ultrasonic transmission surface of said ultrasonic transmissionunit having a high ultrasonic transmission frequency has a largerinclination angle with respect to the conveyance path, compared to theultrasonic transmission surface of said ultrasonic transmission unithaving a low ultrasonic transmission frequency.
 5. The multi-feeddetection apparatus according to claim 2, wherein said respectiveultrasonic transmission unit are arranged at different ultrasonictransmission angles with respect to said ultrasonic reception unit whenviewed from a direction perpendicular to the ultrasonic receptionsurface of said one ultrasonic reception unit.
 6. The multi-feeddetection apparatus according to claim 5, wherein said respectiveultrasonic transmission unit are arranged with a positional relationshipin which respective ultrasonic transmission directions to said oneultrasonic reception unit become perpendicular to each other.
 7. Themulti-feed detection apparatus according to claim 1, wherein saidultrasonic transmission unit and said ultrasonic reception unit havedifferent inclination angles with respect to the conveyance path.
 8. Themulti-feed detection apparatus according to claim 1, wherein saidultrasonic reception unit is arranged to have an outer shape smallerthan an outer shape of said ultrasonic transmission unit.
 9. Themulti-feed detection apparatus according to claim 1, wherein theultrasonic reception surface of said ultrasonic reception unit issmaller than the ultrasonic transmission surface of said ultrasonictransmission unit.
 10. The multi-feed detection apparatus according toclaim 1, wherein the ultrasonic reception surface of said ultrasonicreception unit is smaller than the ultrasonic transmission surface ofsaid ultrasonic transmission unit and is positioned in a region wherethe ultrasonic reception surface faces the ultrasonic transmissionsurface.
 11. The multi-feed detection apparatus according to claim 1,wherein the multi-feed detection apparatus includes a conveyance pathforming plate configured to separate said ultrasonic transmission unitfrom the conveyance path and form at least part of the conveyance path,a through hole is formed at a portion of the conveyance path formingplate that faces said ultrasonic transmission unit, and an opening ofthe through hole is smaller than the ultrasonic transmission surface ofsaid ultrasonic transmission unit.
 12. The multi-feed detectionapparatus according to claim 1, wherein said ultrasonic reception unitincludes a MEMS element which includes an ultrasonic receiving unithaving the ultrasonic reception surface and a holding portion configuredto hold the ultrasonic receiving unit, and is formed on a substrate. 13.The multi-feed detection apparatus according to claim 1, wherein saidultrasonic transmission unit is arranged below the conveyance path, andsaid ultrasonic reception unit is arranged above the conveyance path toface said ultrasonic transmission unit.
 14. The multi-feed detectionapparatus according to claim 1, wherein said ultrasonic reception unitis connected to signal amplification unit for amplifying a receivedreception signal, and said multi-feed determination unit determines,based on a signal waveform output from the signal amplification unit,whether multi-feed of sheet members has occurred.
 15. The multi-feeddetection apparatus according to claim 1, wherein said ultrasonictransmission unit includes a plurality of ultrasonic transmission unithaving different ultrasonic transmission frequencies, and the multi-feeddetection apparatus further comprises selection unit for selecting, fromsaid plurality of ultrasonic generation unit, at least one ultrasonicgeneration unit for transmitting an ultrasonic wave.
 16. The multi-feeddetection apparatus according to claim 14, wherein said ultrasonictransmission unit includes a plurality of ultrasonic transmission unithaving different ultrasonic transmission frequencies, and the signalamplification unit changes an amplification condition of the receptionsignal based on a frequency transmitted from at least one ultrasonictransmission unit among said plurality of ultrasonic transmission unit.17. A multi-feed detection apparatus comprising: an ultrasonictransmission unit, arranged on one side of a conveyance path configuredto convey a sheet-like member, for transmitting an ultrasonic wavetoward the conveyance path; an ultrasonic reception unit, arranged onthe other side of the conveyance path, for receiving the ultrasonic wavefrom said ultrasonic transmission unit; and a multi-feed determinationunit for determining, based on a reception result of the ultrasonic wavereceived by said ultrasonic reception unit, whether multi-feed ofsheet-like members has occurred, wherein said ultrasonic transmissionunit and said ultrasonic reception unit have different inclinationangles with respect to the conveyance path.
 18. A sheet conveyanceapparatus comprising: a multi-feed detection apparatus arranged in aconveyance apparatus main body configured to convey a sheet-like memberalong a conveyance path, wherein said multi-feed detection apparatuscomprising: an ultrasonic transmission unit, arranged on one side of aconveyance path configured to convey a sheet-like member, fortransmitting an ultrasonic wave toward the conveyance path; anultrasonic reception unit, arranged on the other side of the conveyancepath, for receiving the ultrasonic wave from said ultrasonictransmission unit; and a multi-feed determination unit for determining,based on a reception result of the ultrasonic wave received by saidultrasonic reception unit, whether multi-feed of sheet-like members hasoccurred, wherein an ultrasonic transmission surface of said ultrasonictransmission unit is inclined with respect to the conveyance path, andan ultrasonic reception surface of said ultrasonic reception unit isarranged to be substantially parallel to the conveyance path.
 19. Asheet processing apparatus comprising: a sheet conveyance apparatus; anda sheet processing unit configured to perform predetermined processingfor a sheet-like member conveyed by said sheet conveyance apparatus,wherein said sheet conveyance apparatus comprising: a multi-feeddetection apparatus arranged in a conveyance apparatus main bodyconfigured to convey a sheet-like member along a conveyance path,wherein said multi-feed detection apparatus comprising: an ultrasonictransmission unit, arranged on one side of a conveyance path configuredto convey a sheet-like member, for transmitting an ultrasonic wavetoward the conveyance path; an ultrasonic reception unit, arranged onthe other side of the conveyance path, for receiving the ultrasonic wavefrom said ultrasonic transmission unit; and a multi-feed determinationunit for determining, based on a reception result of the ultrasonic wavereceived by said ultrasonic reception unit, whether multi-feed ofsheet-like members has occurred, wherein an ultrasonic transmissionsurface of said ultrasonic transmission unit is inclined with respect tothe conveyance path, and an ultrasonic reception surface of saidultrasonic reception unit is arranged to be substantially parallel tothe conveyance path.